Allylsilanes
Allylsilanes
Allylsilanes
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Scheme 25 <strong>Allylsilanes</strong> from Trimethyl[2-(phenylsulfonyl)ethyl]silane [109,110]<br />
SiMe 3<br />
1. PhSH, AIBN<br />
2. H2O2 O O<br />
S<br />
Ph<br />
54<br />
SiMe 3<br />
1. BuLi<br />
2. R1R2CO 3. MsCl<br />
4. 6% Na/Hg<br />
R1 ,R2 = (CH2) 3 95%<br />
R1 ,R2 = (CH2) 4 94%<br />
R1 = R2 = Ph 95%<br />
R1 = H; R2 = Ph 92%<br />
(2-Cyclopentylideneethyl)trimethylsilane [55,R 1 ,R 2 = (CH 2) 4]; Typical Procedure: [109]<br />
1.6 M BuLi in hexane (40 mL, 64 mmol) was syringed slowly into a suspension of sulfone<br />
54 (15 g, 62 mmol) in anhyd Et 2O (70 mL) at ±708C. The white suspension changed immediately<br />
to a pale yellow soln. After the mixture had stirred for 25 min, cyclopentanone<br />
(5.4 g, 62 mmol) was added. The soln was warmed to rt over 20 min, cooled to ±108C, and<br />
MsCl (7.1 g, 62 mmol) in anhyd Et 2O (5 mL) was introduced. A white precipitate of LiCl<br />
formed instantly. The suspension was refluxed for 25 min, cooled, diluted with Et 2O<br />
(100 mL), washed with aq NaCl, dried (MgSO 4), filtered, and concentrated. The colorless<br />
residue was dissolved without further purification in a mixture of MeOH (50 mL) and<br />
Na 2HPO 4 (35.2 g, 0.25 mol). After the resulting suspension had been cooled to ca. 0 8C, 6%<br />
Na/Hg amalgam (75 g) was added in small portions. The reductive elimination was completed<br />
in 1 h. The suspension was diluted with Et 2O, decanted, and the solvent was removed<br />
in vacuo. The residue was diluted with petroleum ether (bp 35±60 8C, 100 mL),<br />
washed with H 2O, dried (MgSO 4), and passed through a short column (silica gel). Removal<br />
of the solvents under reduced pressure gave the product; yield: 9.8 g (94%).<br />
4.4.40.13 Method 13:<br />
Formation of Exocyclic <strong>Allylsilanes</strong> by the Ramberg±Bäcklund Reaction<br />
Six-membered exocyclic allylsilanes with a variety of substituents â to silicon have been<br />
prepared bythe Ramberg±Bäcklund alkenation reaction of á-sulfonyl sulfones. [112] For example,<br />
treatment of bis-sulfone 57 with butyllithium at ±788C, followed bywarming to<br />
room temperature, yields allylsilane 58 (R 1 = H) (Scheme 26). [112] If the lithiated sulfone<br />
from 57 is alkylated, and a second equivalent of butyllithium is added, â-substituted allylsilanes,<br />
for example, 58 (R 1 = Me, Bn), maybe synthesized bythis protocol. Bis-sulfone 57<br />
is available from cyclohexyl phenyl sulfone (56) bylithiation followed bysulfenylation<br />
and oxidation with 3-chloroperoxybenzoic acid.<br />
Scheme 26 Preparation of Exocyclic <strong>Allylsilanes</strong> by the Ramberg±Bäcklund Reaction [112]<br />
O<br />
O<br />
Ph<br />
S H<br />
56<br />
FOR PERSONAL USE ONLY<br />
854 Science of Synthesis 4.4 Silicon Compounds<br />
1. BuLi<br />
2. Me3Si(CH2)2STs 3. MCPBA<br />
O O O O<br />
Ph<br />
S S<br />
57<br />
SiMe3<br />
1. BuLi, −78 oC 2. R1X, −78 to −20 oC 3. BuLi, −78 to 25 oC R 2<br />
R 1<br />
R 1<br />
R1 = H 80% (step 1 only)<br />
R1 = Me 69%<br />
R1 = Bn 80% 58<br />
Sarkar, T. K., SOS, (2002) 4, 837. 2002 Georg Thieme Verlag KG<br />
55<br />
SiMe 3<br />
SiMe 3